Can I use the Baited Hook ability in response to a spell?

No, you cannot use Baited Hook in response to a spell.

According to Rule 150.2, the activated ability of Gear can only be executed during your own Main Phase while the game state is Open (i.e., when there is no chain).

Because Baited Hook does not have the Reaction keyword (which would allow it to be activated during a Closed State/on an opponent's turn), it cannot be activated in response to a spell or any other chain item.